We have precisely measured the D1 lines of lithium atoms in a collimated atomic beam by high-resolution laser spectroscopy.
We used an external cavity diode laser system (ECDL) stabilized by a Fabry-Perot cavity as the light source to study the lithium D lines. A second ECDL is frequency-stabilized by I2 transition for reference. Laser induced fluorescence was detected and the beat frequency between the two ECDL was recorded as the spectroscopy laser was scanned across the atomic resonance. We obtained the hyperfine splittings of 7Li D1 lines, while the D2 lines were not resolved.
The results for the 2S1/2 and 2P1/2 hyperfine structure interval are 803.540 ± 0.024 and 91.908 ± 0.006 MHz respectively. It is consistent with previous measurements.

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